measure the length of the spring and the coil diameter. Then check with Speedway to see if you can find a spring to match. I have a spring tester so I can measure the spring rate which helps in picking the correct spring.
I use a 375# spring in the front. Not to soft or to hard.
They list 22 spring in the 375 lb rate for under $100 pair.
There is a lot to springs on a Cobra not like buying a replacement fuel pump especially if you can a cut down spring to start with.
Dwight
hope this helps
coil springs from Speedway Motors, America's Oldest Speed Shop
Garage Sale - Spring For Mustang II Coil-Over, 375 Rate - Speedway Motors, America's Oldest Speed Shop